When a concrete building is demolished, the demolished concrete is transported in small pieces by trucks to a concrete recycling facility. The concrete material is crushed and transferred to a conveyor where magnets are used to remove metallic objects from the crushed concrete. Large non-metallic material is removed manually. After these processes, what is typically left is concrete crushed to about 80 mm minus, meaning concrete particles having a dimension of 80 mm or less. The crushed concrete is separated using multiple deck grated screens into different sizes of 80 mm plus (>80 mm), 20 mm (having a dimension of 80-20 mm), 10 mm (20-10 mm) and minus 10 mm (“dust”). Material which is 80 mm plus is returned by conveyor to a secondary crusher to be crushed again and then returned to the screens for sizing.
Generally, recycled 80 mm minus, 20 mm minus and dust concrete can be used again in the building of new buildings or for other purposes. The crushed concrete however is contaminated with large amounts of foreign material such as timber, plastics, light aluminum, wire, asbestos, and other material.
Numerous apparatus and methods for removing impurities from crushed recycled concrete have been proposed. However, the current methods are either not effective or too expensive to be commercially viable.